1. Field of the Invention
This invention relates to a device for preventing a gland nut used in a valve such as a ball valve from loosening as a consequence of rotation of the valve.
2. Description of Prior Art
Heretofore, a device illustrated in FIGS. 6 and 7 has been known as a means to effect the kind of prevention of interest herein.
This preventive device has found utility in a ball valve such as is provided with a fitting flange for fixing an actuator. This ball valve is adapted to open and close a ball by rotating a stem, accommodate packing in a packing chamber specifically provided in the fitting flange as a shaft sealing structure for the stem, and press this packing by tightening through a gland the packing with a hexagonal nut 1 helically coupled with the stem.
This hexagonal nut 1 has the helical union between itself and the stem loosen as a consequence of the opening and closing motion of the valve. Therefore, this loosening of the nut 1 is prevented by a lock plate 3. As illustrated in FIG. 6, the lock plate 3 has a pair of opposite engaging faces 2 engage with the opposed lateral faces of the hexagonal nut 1 and forms therein a fitting hole 5 provided with a pair of opposite engagement faces 4 fit for the stem, thereby enabling the nut 1 to be fixed to the stem.
According to this conventional device, however, since the lock plate 3 has the engaging faces 2 thereof engage with the two opposed faces of the hexagonal nut 1, the lock plate 3, detached from the nut 1, has to be re-attached to the nut 1 each time the nut 1 is rotated by an angle of 60 degrees in order to lock the nut 1 and the stem.
When the hexagonal nut 1 fitted with the lock plate 3 is used to tighten the packing, therefore, the nut 1 must be rotated by an angle of 60 degrees from the position of the lock plate 3. The device, as an inevitable consequence, entails such problems as enabling the tightening of the packing by the nut 1 to be only adjusted every 60-degree rotation of the nut 1 and requiring a considerable tightening force in order to ensure the 60-degree rotation.